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In the horizontal, the Arakawa-C grid is used. In the vertical, the Charney-Phillips grid - see graphic below.
The model levels are hybrid levels. They are terrain following at the surface and gradually change to follow pressure levels at the model top.
For more information have a look at the following publication:
Girard, C., A. Plante et al., 2014: Staggered Vertical Discretization of the Canadian Environmental Multiscale (GEM) Model Using a Coordinate of the Log-Hydrostatic-Pressure Type. Monthly Weather Review, DOI: 10.1175/MWR-D-13-00255.1